Why does this fail on FB 1.5.2?

Directory /opt/firebird/rxs_log is owned by user firebird and group
firebird

Firebird.conf:
ExternalFileAccess = Restrict /opt/firebird/rxs_log

SQL:
RECREATE TABLE EXCEPTION_LOG
EXTERNAL FILE '/opt/firebird/rxs_log/EXCEPTION_LOG'
(
XCEPT VARCHAR( 32) NOT NULL COLLATE ISO8859_1,
MSG VARCHAR( 72) COLLATE ISO8859_1,
GDS_CODE INTEGER,
SQL_CODE INTEGER,
CUR_USER VARCHAR( 128) NOT NULL COLLATE ISO8859_1,
CUR_ROLE VARCHAR( 31) NOT NULL COLLATE ISO8859_1,
TX_TS TIMESTAMP DEFAULT CURRENT_TIMESTAMP NOT
NULL,
ACTUAL_TS TIMESTAMP DEFAULT 'NOW' NOT NULL
);

Error:
ISC ERROR CODE:335544831
ISC ERROR MESSAGE:
Access to external file "/opt/firebirdSS-1.5.1/rxs_log/EXCEPTION_LOG" is
denied by server administrator


At first I used relative paths for the create statement:

RECREATE TABLE EXCEPTION_LOG
EXTERNAL FILE 'rxs_log/EXCEPTION_LOG'

But Firebird wanted to create the file in the /tmp directory. Is there
any way to get it to start relative paths from the directory it is
installed in?